1. Field of the Invention
The present invention relates to a throttle control apparatus mounted on an internal combustion engine, and more particularly to a throttle control apparatus which controls an opening of a throttle valve by a driving source such as a motor activated in response to operation of an accelerator operating mechanism, and which performs various control operations such as automatic speed control operation or the like.
2. Description of the Prior Art
In general, a throttle valve for use in an internal combustion engine is provided to regulate a mixture of fuel and air in a carburetor, or regulate an intake air flow in an electronic fuel injection control system so as to control the output of the internal combustion engine, and is so structured to gear with an accelerator operating mechanism including an accelerator pedal.
Conventionally, the accelerator operating mechanism has been mechanically connected to the throttle valve, whereas an apparatus for opening and closing the throttle valve, or controlling an opening of the throttle valve by a driving source such as a motor in response to operation of the accelerator pedal has been proposed recently. For example, Japanese Utility Model Laid-open Publication No. Sho 60-122549 discloses, as a prior art, a fuel injection system which detects a depressed amount of an accelerator pedal and an opening angle of a throttle valve, and which drives an actuator in accordance with a difference between the detected results to adjust the opening angle of the throttle valve to an angle corresponding to the depressed amount of the accelerator pedal. With respect to the prior art, it has been considered in the above-identified publication that there may be a case where it will become difficult to control the opening of the throttle valve in accordance with an accelerator pedal signal due to a malfunction of the actuator or a poor movement of a throttle valve by some reasons. In view of the case, proposed in the above-identified publication is an apparatus, wherein if it is determined that the difference between the accelerator pedal signal and the throttle valve signal exceeds a predetermined value and that the time period of the difference continuously exceeding the value is longer than a predetermined time period, the injection of fuel or the ignition to the engine will be stopped.
In the publication of 60-122549, however, when the accelerator pedal is in a depressed condition thereof, it is not necessarily appropriate to stop the injection of fuel or ignition provided that the time period of the difference exceeding the predetermined value is longer than the predetermined time period. In the case where the accelerator pedal is in the depressed condition, there may be many cases where the operation of the engine should be continued. Rather, it is appropriate to control the engine to lessen its power or stop it, only when the accelerator pedal has been released to return to its initial position.
The apparatus disclosed in the above-identified publication is so controlled that the engine is stopped when the time period of the difference exceeding the predetermined value exceeds the predetermined time period. However, this will cause too much operation in the case where only a small malfunction or the like has occurred so that the engine can be easily recovered therefrom. In this case, therefore, it is appropriate to disengage the actuator from the throttle valve temporarily, so as to enable the engine to operate immediately after it has been recovered.